Structural evolution of bias sputtered LiNi0.5Mn1.5O4 thin film cathodes for lithium ion batteries

• LiNi0.5Mn1.5O4 thin films have been deposited on stainless steel substrates.
• Various negative biases were applied on the substrates during deposition.
• The particle sizes of LNMO thin films decrease with increasing negative bias.

LiNi0.5Mn1.5O4 (LNMO) thin films have been deposited on stainless steel substrates using radio frequency (f = 13.56 MHz) magnetron sputtering, followed by thermal annealing in ambient atmosphere. Various negative biases were applied on the substrates during deposition. The structural evolution of LNMO thin films under different negative biases has been investigated and characterized by X-ray diffraction. All of the deposited films exhibit a crystalline spinel structure with a space group of Fd-3m, which is a so-called disordered phase. The results also indicate that particle size decreases with increasing negative bias. The electrochemical properties of the LNMO thin films as cathode materials for lithium ion batteries were investigated. Two distinctive voltage plateaus at ~ 4.7 V and at ~ 4.0 V (vs. Li+/Li) can be observed in the discharge curves, corresponding to the reactions of the disordered phase. The capacity of LNMO thin film electrodes under suitable negative bias can be optimized.